1. Field of the Invention
The present invention relates to a gold-cobalt based amorphous alloy plated film useful as a plated film for terminals of component parts of electric apparatuses and excellent in electrical and mechanical properties, an electroplating bath capable of being used to form the gold-cobalt based amorphous alloy plated film, and an electroplating method conducted by use of the electroplating bath.
2. Prior Art
At present, gold plated films called the hard gold plated film are widely used as an electric contact material in electric and electronic component parts such as connectors, small-sized relays, printed wiring boards, etc., particularly at portions required of high reliability. The hard gold plated film contains cobalt, nickel or the like added to gold so as to enhance the hardness of the plated film without lowering the good conductivity and chemical stability which are intrinsic of gold. The hard gold plated film has a microstructure in which microcrystals (20 to 30 nm) of gold are bound, and the microstructure is considered to provide the hardness (in terms of Knoop hardness Hk, about 170) which is needed at minimum for obtaining the wear resistance required of contact material.
On the other hand, attendant on the reduction in size of electronic component parts in recent years, the size of the electric contacts has also been reduced, and the plated films formed on such micro contacts have also been reduced in size and film thickness. Therefore, there is a request for a further enhancement of the hardness of the plated films in order to attain a higher wear resistance.
In addition, it is considered that the size of contacts will approach the size of microcrystals in the above-mentioned hard gold plated film in the near future. In the case where the hard gold plated film is formed on such a micro contact, the absolute number of the microcrystals constituting the plated film will be small. In such a case, therefore, it is expected to be impossible to attain the same level of durability as in the case of forming the hard gold plated film on a contact having the size which is applied at present.